Abstract
The control of toxic nitrogenous compounds such as ammonia and nitrite is well established as part of farm management protocols for indoor Litopenaeus vannamei aquaculture. In comparison, nitrate (NO 3 -N) levels are often disregarded due to relative low toxicity to shrimp, as evidenced by the lack of studies on chronic nitrate stress. In the current study, 160 individuals of L. vannamei in the grow-out stage were exposed to 50 mg/L NO 3 -N (LN) and 400 mg/L NO 3 -N (HN) for 28 days. After exposure, growth performance, physiological stress markers and morphological abnormalities were assessed. Morphological abnormalities and injuries were measured using a health score based on the integrity of antennae, eyes, rostrum, legs (pleopods and pereiopods), uropods/telson, exoskeleton, gills, and hepatopancreas. No difference was detected in the survival rate between treatments. However, HN impacted shrimp growth performance and feed conversion reducing SGR, biomass, daily weight gain and increasing FCR. No significant differences were observed in the physiological parameters analyzed in the hemolymph (glucose, lactate, total proteins, hemocyanin, and hemocyte count) and in the hepatopancreas (superoxide dismutase activity). Congruently, the health index revealed no significant difference, with only the hepatopancreas quality mildly impaired in the HN group. Chronic 400 mg/L NO 3 -N exposure reduces growth performance and feed utilization, as energy appears to be redirected to maintain homeostasis, and has a minor impact on shrimp welfare. Graphical Abstract